1. Field of the Invention
This invention relates to a HIP-bonded body comprised of a beryllium member and a copper member, as well as a method of producing the same.
2. Description of the Related Art
Recently, in various application fields such as neutron reflector of material testing reactor, neutron accelerator and the like, beryllium is considered to be a prominent material in view of its high neutron reflection ratio. While beryllium itself has a relatively good thermal conductivity, when a beryllium member is used under a severe thermal load condition, the beryllium member is often bonded to a copper alloy member to provide an even higher thermal conductivity. As a method for bonding beryllium member and copper alloy member, HIP bonding method is considered to be a highly probable candidate.
Heretofore, when a beryllium member and a copper alloy member are bonded by HIP method, it has been considered necessary to carry out the HIP process under a high temperature of not less than 700.degree. C. This is because there usually exists a beryllium oxide film on the beryllium surface, and a desired bonding by interdiffusion of beryllium and copper alloy is not sufficiently achieved unless the beryllium and the copper alloy members are heated to a temperature of not less than 700.degree. C. With such a bonding method, however, there may be instances wherein copper and beryllium members are separated from each other at their interfaces due to heat cycles during operation. Such separation is often due to the presence of brittle intermetallic compounds, such as Be.sub.2 Cu, BeCu, which tend to be formed at the interface between beryllium and copper members under the high temperature condition. Moreover, the HIP bonding process performed under a high temperature condition is not very appropriate in view of cost and energy consumption.
From such viewpoint, it would be feasible to remove the oxide on beryllium surface in vacuum atmosphere and subsequently form a pure copper film on the purified beryllium surface, by ion plating and the like. In this case, it would be possible to achieve a strong bonding of beryllium and copper alloy members even under a low HIP temperature of 400 to 550.degree. C., since oxides are excluded at the interface between the pure copper and beryllium members and intermetallic compounds are not formed at the interface between the two members. However, even when the beryllium and copper alloy members are bonded to each other in the above-mentioned manner, when the bonded body is used under a temperature of not less than 400.degree. C, brittle intermetallic compounds of beryllium and copper tend to be formed at the interface where intermetallic compounds had not been formed during the bonding process, with the result that the bonded body may be broken at the interface.
To eliminate the above-mentioned problems, the beryllium member may be provided with a soft metal layer, e.g., an aluminum layer, which does not form intermetallic compounds with beryllium, such that the soft metal layer is bonded to the copper alloy member. On the other hand, however, when an aluminum layer is bonded to the copper alloy member, a satisfactory bonding may not be achieved due to brittle compounds of aluminum and copper which are formed at the interface between the copper alloy member and the aluminum layer. Therefore, in this case, it is important to interpose an aluminum-beryllium diffusion inhibition layer such as titanium, at the interface between the aluminum layer and the copper alloy member. In other words, it would be necessary to provide an aluminum intermediate layer for the beryllium member and a titanium intermediate layer for the copper alloy member. However, even when the intermediate layers such as aluminum and titanium layers are provided for the beryllium member and copper alloy member, respectively, it is still difficult to obtain a strongly bonded state because aluminum and titanium are active metals and their surfaces thus tend to be readily oxidized.
Moreover, when a metallic foil is used as an intermediate layer in a conventional manner, it is difficult or practically impossible to obtain a strongly bonded state as a result of oxide films on its surfaces. Also, when the metallic foil is applied to relatively complex structural member, the metallic foil tends to be dislocated relative to the beryllium member or copper alloy member or wrinkles may occur, even when the metal foil is combined with titanium foil or copper foil, so that a reliable bonding is still difficult to achieve.